The joint that gets mistaken for the lower back
The sacroiliac joints sit where the base of the spine meets the pelvis, one on each side. They move very little, and their job is to transfer load between the spine and the legs.
When one becomes a source of pain, the pattern it produces - low, to one side, often referring into the buttock and down the thigh - looks a great deal like a lumbar disc or nerve problem. That resemblance is the whole difficulty. It is a recognized cause of persistent low back pain and a common reason for treatment aimed at the lumbar spine not delivering what was hoped.
Why it is easy to miss
An MRI of the lumbar spine will nearly always show something, because disc changes and wear appear on the scans of plenty of people who have no pain at all. Once a finding is on the screen it is easy to attribute the symptoms to it and look no further.
Two situations should raise the question specifically: pain that has not responded to properly delivered lumbar treatment, and pain that persists or appears after lumbar surgery. Fusing part of the lumbar spine shifts load onto what sits below it, and the sacroiliac joint is directly in that path.
How it is identified
Examination tests exist, and several used together are more informative than any one of them. But the answer that a plan can be built on usually comes from a diagnostic injection: local anesthetic placed into the joint under image guidance, and a careful note of what your usual pain does over the following hours.
Meaningful temporary relief implicates the joint. Little change points elsewhere and saves you from a treatment aimed at the wrong target. Either result is useful, which is why this step comes before decisions rather than after them.
What can be done
In steps, and in this order.
- Address the mechanics. Physiotherapy and manual treatment for the muscles and movement patterns around the pelvis. For many people this is enough.
- Settle the joint. A therapeutic injection can reduce inflammation and give a window in which rehabilitation is easier.
- Treat the nerves that carry the pain. Where relief from injection is real but short-lived, targeting the small nerves supplying the joint can extend it considerably.
- Fuse the joint. Considered only when the source is confirmed, the pain is persistent, and the steps above have not held. It is done through small incisions, usually as a day case or an overnight stay.
If the joint is not the source
That is a genuinely useful finding, not a wasted appointment. If numbing the joint changes nothing, the pain is coming from somewhere else, and the search moves on with one significant possibility properly excluded - which is more than most people arrive with.
Where the lumbar spine turns out to be the source, lower back care covers what follows. Where nothing structural explains the picture, non-surgical care and rehabilitation are usually the right route.
Conditions in the sacroiliac joint
These are the problems that bring people to us for sacroiliac joint surgery. Each one explains what it is and how it is treated, surgery included or not.
Procedures used in the sacroiliac joint
Ordered from least to most invasive. Which one fits is decided from your imaging and examination, not chosen from a list.
Common questions
How do I know whether my pain is coming from the sacroiliac joint?
You often cannot tell from symptoms alone, which is the central difficulty. Sacroiliac pain typically sits low and to one side, around the dimple above the buttock, and can refer into the buttock and thigh - a pattern that overlaps closely with a lumbar disc or nerve problem. Examination tests help but none is conclusive on its own. The most reliable answer usually comes from a diagnostic injection: if numbing the joint temporarily removes the pain, the joint is implicated.
Why is it so often missed?
Because it looks like a lower back problem and the lower back is where people look. An MRI of the lumbar spine will usually find something - disc changes are common in people with no pain at all - and it is easy to attribute the symptoms to that finding and stop. The sacroiliac joint is a recognized source of persistent low back pain, and it is worth considering particularly when lumbar treatment has not helped, or when pain persists after lumbar surgery.
What is a diagnostic injection and what does it prove?
Local anesthetic is placed into the joint under image guidance, and you are asked to note how your usual pain behaves over the following hours. Substantial temporary relief points to the joint as a source; little change points away from it. It is a diagnostic step as much as a treatment, and a considered plan usually rests on it rather than on imaging alone.
What can be done if the joint is confirmed as the source?
Usually in steps. Physiotherapy and manual treatment addressing the mechanics around the pelvis come first, often with an injection to settle inflammation. Where relief is real but short-lived, treating the small nerves that carry pain from the joint can extend it. Fusion of the joint is considered only when the problem is confirmed, persistent, and has not responded to those steps - it is the last option here, not the first.
Does sacroiliac pain happen after lumbar fusion?
It can. Fusing part of the lumbar spine transfers load to the levels and joints below it, and the sacroiliac joint sits directly in that path. It is one of the recognized reasons for pain that persists or appears after an otherwise technically successful fusion, and it is worth investigating specifically rather than assuming the fusion has failed.
Is sacroiliac joint fusion a major operation?
It is smaller than a lumbar fusion. It is generally done through small incisions with implants placed across the joint, often as a day case or a single overnight stay, with a recovery of roughly six to twelve weeks. That said, it is still a fusion - it permanently stops the joint moving - so the case for it should be firmly established before proceeding, which is why the diagnostic steps matter.